1. Field of the Invention
This invention relates to a laser-based tool for processing materials. In one aspect, this invention relates to a laser material processing tool for use in wellbore drilling. In another aspect, this invention relates to a laser material processing tool for material cutting. In another aspect, this invention relates to a laser material processing tool for material spalling. In yet another aspect, this invention relates to a laser material processing tool for material thermal treatment, e.g. annealing. In yet another aspect, this invention relates to a laser material processing tool for material curing. In yet another aspect, this invention relates to a laser material processing tool for material surface conditioning.
2. Description of Related Art
Fluid flow into a completed subterranean wellbore is initiated by perforation of the well casing or liner. Conventionally, such perforations are created using shaped charges for establishing flow of oil or gas from the geologic formations into the wellbore. This generally creates tapered, uneven shaped openings of relatively small diameter, i.e. less than about 1 inch. In addition, the perforations typically extend only a few inches into the formation. In addition to the limitations of opening size and hole depth, there are numerous problems with this approach. First, the melt or debris from shaped charges usually reduces the permeability of the producing formations resulting in a substantial reduction in production rate. Second, these techniques involve the transportation and handling of high power explosives and are causes of serious safety and security concerns. Third, the energy jet into the formation also produces fine grains that can plug the pore throat, thereby reducing the production rate. Water jetting can also be used for wellbore perforation; however, the opening that is created is generally not very uniform.
Additionally, other steps for initiating fluid flow may also be required, depending, at least in part, on the physical properties of the fluid in question and the characteristics of the rock formation surrounding the well. Fluid flow may be inhibited in situations involving highly viscous fluids and/or low permeability formations. Highly viscous fluids do not flow easily. As a result of the decreased rate of flow, efficiency is lowered and overall production rate decreases. The same is true for low permeability formations. In extreme cases, these factors reduce the flow rate to zero, halting production entirely.
The use of lasers for the purpose of producing boreholes to enable the extraction of liquid and gaseous fuels from underground formations is well-known in the art. U.S. Pat. No. 4,066,138 to Salisbury et al. teaches an earth boring apparatus mounted above ground that directs an annulus of high powered laser energy downwardly for boring a cylindrical hole by fusing successive annular regions of the stratum to be penetrated at a power level that shatters and self-ejects successive cores from the hole.
U.S. Pat. No. 4,282,940 to Salisbury et al. teaches a method for perforating oil and gas wells. Using this method, a high-powered coherent light beam is axially directed along the borehole to a predetermined depth and deflected along a beam axis. The beam is focused to concentrate at each of a plurality of spaced focal points along the deflected beam. This, in turn, is said to provide a significant increase in the distance that calculated oil or gas bearing formations can be perforated, thereby increasing the yield by more conventional means.
With known laser-based devices for wellbore perforation, perforation depths have been limited to about 4 inches after which further penetration is hampered by hole taper issues and the lack of efficient debris removal. Hole taper occurs when a collimated laser beam is utilized because of the Gaussian beam shape distribution and attenuation of the laser beam with the debris column in the hole. The edges of the beam contain less irradiance than the center of the beam as a result of which, as the perforation gets deeper, the hole eventually comes to a point and the laser beam can no longer penetrate. In addition, once begun, hole tapering is difficult to correct with a laser processing beam oriented parallel to the perforation axis due to the increased surface area presented by the side walls. Furthermore, reflections from grazing angle incidence tend to reflect laser energy into the central regions of the opening/perforation, creating excessive heating in the center, causing uneven material removal, opening shapes, and opening quality. In rock/refractory applications, the central material could glassify before the sidewall material is spalled, thereby creating poor quality openings and reducing the efficiency of material removal.
Drill lasers emit short, high-frequency light pulses for creating boreholes. The high amount of local energy that is generated is used to remove the material or produced in the borehole due to abrupt vaporization while the molten phase is avoided. However, with conventional drill lasers, there is also the possibility that melt residue or slag deposits on the edge of the borehole. Such melt or slag residue deposits are undesirable because they can significantly influence the borehole quality.